An internal combustion engine (hereinafter, simply referred to as “engine”) needs to be driven by a starting apparatus (hereinafter, pertinently referred to as “starter”) in starting the engine. As the starting apparatus, there are a gear type starter, a belt type starter and the like all of which are common in that an electric motor constitutes a drive source.
In starting the engine, comparatively large torque is required although depending on a kind and a displacement thereof. Therefore, when the engine is cranked directly by the motor, the physical configuration of the motor naturally becomes large. Hence, in a recent starting apparatus requesting light-weighted compact formation, high torque necessary for starting is achieved by interposing a reduction gear between the motor and the engine to thereby increase a speed reducing ratio.
Although there are various reduction gears, a planetary gear-type reduction gear, which compactly achieves a large speed reducing ratio, is frequently used. In the planetary-type reduction gear, a driving force inputted from the motor to a sun gear of the reduction gear is outputted from a carrier supporting planetary gears with high torque. In this case, rotation of an internal gear, which meshes with the planetary gears, in the circumferential direction is restricted to achieve a predetermined speed reducing ratio. That is, a large reaction force (torque) produced in accordance with the output needs to be received by the internal gear. Therefore, rotation of the internal gear in the circumferential direction needs to be constrained.
Meanwhile, according to the engine, torque necessary for rotation is rapidly varied by strokes of intake, compression and the like and an engine rotation speed is also pulsated. The motor of the starter cannot well follow such a load variation or the like and therefore, impact load is applied between the internal gear and a rotation restricting portion thereof. Further, the reaction force applied to the internal gear is not constant. As a result, unpleasant sound is likely to be caused in starting the engine due to vibration or the like of the internal gear by simply constraining the internal gear.
When the internal gear is rigidly restricted here, it is required to reinforce the internal gear or the restricting portion to be able to withstand the shock load, which hampers light-weighted compact formation of the starter. Hence, in order to alleviate the shock load applied to the internal gear and the like, a shock absorbing member including an elastic body made of such as rubber is provided between the internal gear and the rotation restricting portion. These are proposed in, for example, JP-Y2-2-31581, JP-Y2-2-31583, JP-B2-4-40549 (U.S. Pat. No. 4,561,316), and JP-A-5-52166 (U.S. Pat. No. 5,323,663).
For example, according to JP-Y2-2-31581, JP-Y2-2-31588 and JP-B2-4-40549, the shock absorbing member is for example provided on an outer peripheral side of an internal gear. However, an outer diameter of a reduction gear is increased thereby and compact formation of a starter is not achieved.
According to JP-A-5-52166, a projection extending from a side face of an internal gear in an axial direction is held by a shock absorbing member (elastic body) and therefore, in this case, a starter is not enlarged in an outer diameter direction. However, the projection of the internal gear is not held elastically by the shock absorbing member from the start. Therefore, shock load is not necessarily alleviated sufficiently from start of operation thereof. Particularly, in the case in which the internal gear and the like are made of synthetic resin in view of light-weighted and low coast formation or the like, when shock load is insufficiently alleviated, reliability of the internal gear and therefore, the starter can be lessened.
Further, in JP-A-5-52166, a friction plate is separately pressed to a pivoting plate engaged with the internal gear and the internal gear is constricted by friction force produced therebetween. Therefore, the structure of the starting apparatus is complicated.
Also, the shock absorbing member used in JP-A-5-52166 is rubber in a shape of a rectangular parallelepiped and an area thereof in contact with an inner wall of a containing portion thereof is large. Therefore, compression operability of the shock absorbing member is poor and the shock absorbing member is likely to easily wear.
Further, the shock absorbing member only receives reaction force in the circumferential direction of the internal gear. There is not a specific disclosure with regard to supporting the internal gear in an axial direction. In addition, the internal gear is not provided with a detent and therefore, the internal gear continues rotating little by little while the exerted reaction force is large. As a result, efficiency of transmitting driving force of the motor is likely to be lessened.